Abstract: Fair multi-party certified mail protocol is a value service to deliver important data over Internet with guaran- teed receipt for each successful delivery. Therefore, the protocol needs to be confidential, and meets non-repudiation, fairness,exclusion and timeliness. This paper pointed out potential security concern for a current protocol,and improved the protocol based on signcryption scheme. The analysis by Kailar logic shows that the protocol can achieve the non-re- pudiation, fairness. Furthermore, it has advantage of resisting the attacks such as distort, replay and conspiracy.

Key words: Multi-party certified e-mail protocol, Non-repudiation, Fairness, Signcryption, Kailar logic